The following abbreviations may be found herein:
3GPPthird generation partnership projectACKacknowledgementCCEcontrol channel elementCRCcyclic redundancy checkDAIdownlink assignment indexDLdownlinkeNBnode B/base stationHARQhybrid automatic repeat requestLTElong term evolutionLTE-Along term evolution advancedNACKnegative acknowledgementOFDMorthogonal frequency division multiplexPDCCHphysical downlink control channelPDSCHphysical downlink shared channelPUCCHphysical uplink control channelPUSCHphysical uplink shared channelRRCradio resource controlSPSsemi-persistent schedulingTDDtime division duplexUEuser equipmentULuplink
LTE wireless communication systems aim to provide enhanced services by means of higher data rates and lower latency with reduced cost. One benefit of deploying LTE TDD systems is to enable asymmetric UL-DL allocations in a radio frame. Typically if more data is to be sent in DL, there can be a higher number of DL subframes in a radio frame to accommodate that greater data volume. In LTE TDD systems, the asymmetric resource allocation is realized by providing seven different semi-statically configured UL-DL subframe configurations for a given radio frame, as specified in Table 4.2-2 of 3GPP TS 36.211 v 10.5.0 (June 2012) which is extracted below.
Uplink-Downlink-downlinkto-Uplinkconfig-Switch-pointSubframe numberurationperiodicity012345678905 msDSUUUDSUUU15 msDSUUDDSUUD25 msDSUDDDSUDD310 ms DSUUUDDDDD410 ms DSUUDDDDDD510 ms DSUDDDDDDD65 msDSUUUDSUUD
These allocations, it can be seen, can provide between 40% and 90% DL subframes, and in conventional practice the UL-DL configuration in use is informed to the UE (and changed) only via system information on the broadcast channel. The UL-DL configuration is only configured semi-statically and so may not adapt to the instantaneous traffic situation. This is inefficient in terms of resource utilization, particularly in small cells/cells with a small number of users where the traffic situation can often change rapidly.
To address this inefficiency, a flexible TDD configuration study item for LTE-A Release 11 was completed. Evaluations in the study item revealed possibly significant performance benefits by allowing TDD UL-DL reconfiguration based on traffic adaptation in small cells. The studies also recommend interference mitigation scheme(s) for systems with TDD UL-DL reconfiguration.
As with asymmetric UL-DL configuration and flexible TDD allocation, there are several challenges to overcome before any implementation may be considered viable. One particular challenge is to allow the reconfiguration of TDD UL-DL configuration on at most a radio frame basis without significant impact on the current 3GPP specification, and to allow coexistence with legacy (i.e. Rel. 8, 9, 10) UEs. It is thought that providing an improved method for PUCCH resource allocation, and for HARQ-ACK concatenation, for use in wireless communication systems that support flexible-TDD UL-DL configuration may help in this regard.
As specified in LTE Rel. 8, 9 and 10 and further illustrated in FIG. 1, one UL subframe is responsible for carrying HARQ-ACK feedback of M DL subframes and/or special subframes, where M is the size of a DL association set as specified in Table 10.1.3.1-1 of 3GPP TS 36.213 (which is the lower table (120) in FIG. 1). In table (120), the DL association set is defined for each UL subframe for different UL-DL configurations. For instance, UL subframe #2 (124) in TDD configuration #3 (125) is responsible for DL transmission which happened k subframes earlier, where the value of k is specified in table (120) by (123), (122) and (121)—that is 7, 6 and 11 subframes earlier. As a result, UL subframe #2 (114) in Frame n+1 is responsible for carrying HARQ-ACK feedback for special subframe #1 (111) (for k=11), DL subframe #5 (112) (for k=7) and DL subframe #6 (113) (for k=6) transmitted in Frame n.
In order to aggregate reserved but unused PUCCH for PUSCH transmission, PUCCH resource for M DL subframes is interleaved. Since at most two OFDM symbols can be used for PDCCH transmission on a special subframe, PUCCH resource for special subframes is mapped later than that of normal DL subframes.
Depicted in FIG. 2 is PUCCH resource reserved in UL subframe #2 in Rel. 10 when UL-DL TDD configuration #3 is used. (211), (221) and (231) is the first CCE (Control Channel Element) and (212), (222) and (232) is the last CCE in PDCCH region of DL subframe #5 (210), DL subframe #6 (220) and special subframe #1 (230), respectively. There is a one-one mapping between CCE index and PUCCH index, and the PUCCH resource for these three DL subframes and special subframes is block interleaved. For instance, PUCCH with index of NPUCCH(1)+10 (241) is associated with PDCCH transmission with first CCE index of 11 in DL subframe #5 (210). PUCCH with index NPUCCH(1)+33 (242) is associated with PDCCH transmission with first CCE index of 12 in DL subframe #5 (210).
As one candidate solution for maintaining HARQ-timing for Flexible-TDD system, HARQ-timing of reference configuration could be followed for HARQ-ACK feedback for Flexible-TDD UEs. For instance, UL-DL TDD configuration #2 could be used as the reference configuration for UL-DL TDD configuration #0, #1, #2, #6 for DL HARQ-ACK timing. As another example, configuration #5 could be used as the reference configuration for all 7 UL-DL TDD configurations.
As illustrated in FIG. 3, in Flexible-TDD system (310), there are at least two kinds of UEs: (i) legacy UEs (312) which are not aware of the Flexible-TDD configuration, and (ii) Flexible-TDD UEs (313) which have knowledge of both legacy TDD configuration by detecting SIB1 information and Flexible-TDD configuration indicated by the eNB explicitly or implicitly. It is highly likely that the Flexible-TDD configuration may be different from the legacy TDD configuration. For instance with reference to FIG. 3, in subframe n−1, the legacy UE is configured with UL-DL TDD configuration #0 (320) while the Flexible-TDD UE is configured with instantaneous UL-DL configuration #2 (330). Assuming UL-DL TDD configuration #2 is used as reference configuration for HARQ-timing for Flexible-TDD UE, then on UL subframe #2, the legacy UE should feedback HARQ-ACK in UL subframe #2 (334) for DL transmission in special subframe #6 (321) and the Flexible-TDD UE should feedback HARQ-ACK for DL transmission in subframe #4 (331), #5 (332), #6 (333) and #8 (334).
As a result, for the same UL subframe, different DL association sets are used by the legacy UE and Flexible-TDD UE. To be specific, in the above example, DL association set containing only special subframe #6 (321) is used by legacy UE and DL association set containing subframes #4 (331), #5 (332), #6 (333) and #8 (334) is used by Flexible-TDD UE. Since PUCCH is reserved according to the DL association set, if Rel. 10 resource mapping is followed directly by Flexible-TDD UE, then PUCCH collision or low PUCCH efficiency may occur.
By way of further explanation, Option 1 (340) (overlap) in FIG. 3 depicts where the same offset value of NPUCCH(1) is used by legacy UEs and Flexible-TDD UEs. Assuming the first CCE index of PDCCH for one legacy UE in special subframe #6 (321) and one Flexible-TDD UE in DL subframe #4 (331) are both 0, then they will both be mapped to the first PUCCH in the dynamic PUCCH region (i.e. (341) for legacy UE and (342) for Flexible-TDD UE) leading to PUCCH collision. Alternatively, Option 2 (350) (no overlap) in FIG. 3 depicts where PUCCH (353) reserved for Flexible-TDD UE is adjacent to PUCCH (351) reserved for legacy UE. Two copies of PUCCH (351,352) are reserved for special subframe #6 (321,333), thus resulting in low PUCCH efficiency.
It is therefore thought that a new PUCCH resource allocation method for Flexible-TDD UEs which reduces or avoids PUCCH collision and/or achieves higher PUCCH resource efficiency may be desirable.
In PTL1 there is determined a first UL-DL configuration for subframes in a frame, which in various examples is fixed or dynamically allocated. A second UL-DL configuration is semi-statically allocated such as in system information. When mapping automatic repeat request signalling for a first UE which is dynamically allocated an UL-DL configuration, at least some DL subframes mapped by the second UL-DL configuration are excluded by the mapping. In one example, UL resources mapped from a first group of DL subframes are indexed according to the second configuration, and then UL resources mapped from a second group of DL subframes are indexed according to the first configuration, and the excluded DL subframes are within the first group and excluded from the second group and the automatic repeat request signalling is in an uplink resource mapped from the second group.
As well as being fed back on PUCCH, HARQ-ACK can be transmitted on PUSCH even when PUCCH format 1a/1b/3 is configured. For instance when a UE receives an UL grant and simultaneous PUSCH+PUCCH transmission is not configured, then HARQ-ACK bits are concatenated, coded and transmitted with UL data on PUSCH. If a reference configuration is followed for HARQ-timing, the concatenation of HARQ-ACK bits for Flexible-TDD system should also be specified.
It is to be clearly understood that mere reference herein to previous or existing apparatus, systems, methods, practices, publications or other information, or to any associated problems or issues, does not constitute an acknowledgement or admission that any of those things individually or in any combination formed part of the common general knowledge of those skilled in the field, or that they are admissible prior art.